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<title>字符串</title>
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<body>
<h1 id="-">字符串</h1>
<hr>

<pre><code>var num1="hello js";
</code></pre><ul>
<li>charAt() 返回下标对应值</li></ul>
<pre><code>console.log("charAt",num1.charAt(0)); \\返回下标为0的对应值
</code></pre><ul>
<li>charCodeAt()   返回10进制的unicode编码 ascii表10进制对应值</li></ul>
<pre><code>console.log("charCodeAt",num1.charCodeAt(0));
</code></pre><ul>
<li>indexOf() 返回字符串片段的开始位置下标，若不存在，则返回-1<br>indexOf 只会返回字符串片段第一次出现的位置,第二个参数表示搜索的起始位置</li></ul>
<pre><code>console.log("indexOf",num1.indexOf("l",4));
</code></pre><ul>
<li>concat 拼接 返回新的字符串 可添加多个</li></ul>
<pre><code>console.log(num1.concat("!","？"));
</code></pre><ul>
<li>返回10进制unicode编码对应的字符串</li></ul>
<pre><code>
onsole.log(String.fromCharCode(104,101)); //得到he
</code></pre><ul>
<li><ol>
<li>slice(开始,结束) 截取字符串的片段</li><li>开始为必选 支持负数(表示倒数第几位)</li><li>结束为可选,不包括自己,如果不写,则到字符串的最后,支持负数(表示倒数第几位) </li></ol>
</li></ul>
<hr>

<pre><code>var  str2 = "hello-word";
</code></pre><ul>
<li><p>substr、substring 截取某一个片段</p>
<ol>
<li>第一个参数 开始的下标</li><li>第二个参数 <ol>
<li>substr:长度</li><li>substring:下标位置(不包含自己)  </li></ol>
</li></ol>
</li><li><p>split 将字符串以某个字符串作为分割点去分割为数组 第二个参数是规定数组的长度</p>
</li></ul>
<pre><code>console.log("split",str2.split("-"));
            ////第二个参数是规定数组的长度
            console.log("split",str2.split("",5));
</code></pre><ul>
<li>concat 数组之间的拼接</li></ul>
<pre><code>var arr=["hello", "word"].concat(["!!"]);
            console.log("数组的串连",arr);
</code></pre><ul>
<li>replace 替换  </li></ul>
<pre><code>var str4="今天是星期天吗";
            console.log(str4.replace("天","日"));
</code></pre><ul>
<li>replace 用正则表达式</li></ul>
<pre><code>console.log(str4.replace(/天/g,"日"));
</code></pre><hr>

<pre><code>var str5="hello";
          var str6="HELLO";
</code></pre><ul>
<li>toUpperCase():将字母变成大写  toLocaleLowerCase():将字母变成小写</li></ul>
<pre><code>console.log("大写",str5.toUpperCase());
          console.log("小写",str6.toLocaleLowerCase());
</code></pre><ul>
<li>trim() 删除前后空格</li></ul>
<pre><code>var str7="    肚子好饿   ";
          console.log(str7.trim().length);
</code></pre>



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